Bottom of print is oversize and has a small lip

Hi,

I'm new to 3D printing and have been doing a lot of testing and tuning to get the printer working well. However I have one problem that I can't seem to fix. On any prints the base seems to be a bit wider than the rest of the print. In this image you should be ale to see the bottom 5 layers are sligtly oversize and gradually reducing in size. By 6th layer size is consistent. Measuring with calipers shows bottom is 2.06cm so 0.6mm oversize and by top box is 1.995cm so 0.05mm undersize

Printed ReprapPrusa I3, Repetier & Slic3r, Ubuntu 14.04. I get a similar problem slicing with Cura but it seems like just one layer is oversize.

Slic3r seems to do this deliberately as it visibly oversizes the first layer in print preview.
Cura doesn't show any oversize in print preview and the lip seems to be just the bottom layer.

I've tried adjusting tempertaure, speed, adding a little to Z offset but I can't seem to get rid of this. I haven't played with feed rate yet because everywhere else looks like feed is spot on.

Any suggetsions?

Thanks, Colin

on slic3r, there is a setting for first layer width. Try reducing that.

That's called "elephant foot". It comes from the the first layer getting squished out thin under the nozzle and the bed temperature being high enough to get the part to stick. If you turn down the bed temperature the problem will be reduced, but the part may not stick to the bed very reliably. The best solution is to design a small chamfer into the base of the part so that the designed base is a little smaller that the rest of the outline of the part. Or you can live with it- it's usually easy to trim off the excess with a razor knife, at least if the object has a base with straight sides.

Edited 1 time(s). Last edit at 11/05/2015 10:56PM by the_digital_dentist.

---

Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

I encountered this as well and there can be a few causes that are not obvious at first sight.
For the start check if the nozzle actually moves that far out for the first layers or if it is just extruding too much.
You can do that by checking the gcode or with a cam that records the first few layers (mark the corner position on the screen).
On the pic it looks like the base is sticking really well and in the right place, so the other factor could be shrinking of the print, ABS and Nylon love to do that....
You can check for that by stopping the print for a bit until the part has cooled down.
When the layer after this pause is far wider than the previous it means your part is actually shrinking.
Although the top should appear slightly wider during the printing in this case.
Last but not least the actual Z- offset for the nozzle and the infill.
Most people home their printer, move the hotend over the plate and "calibrate" the zero Z-heigth this way.
I prefer the other way:
Start a print and stop it once the first layer starts to print.
Measure the distance between nozzle and plate with shims or the old postcard - whatever you prefer.
Reason for this simple, the nozzle is hot, so no plastic interferes with the measurement as you can push it away.
Also any offset that you might not have noticed will be applied.
Keep in mind that when you calibrate from the home position with a 0.1mm shim that you also start printing 0.1mm above the bed!
But if you calibrate from an interrupted first layer you get the actual print height - which means for a 0.2mm first layer you calibrate with a 0.2mm shim
The first layer is usually printed with a solid infill, same for the layers after.
If the infill is too much or the first layer not calibrated properly the excess plastic will go somewhere - usually outwards....
Since this is true for the next solid layers well the print can "expand".
You can see that already on the first layer.
The lines should be smooth and well defined, if they have a wave pattern on the open side or you see plastic being pushed up between the lines then there is too much extrusion happenening.

Didn't read DownUnder's suggestions, but my first thought...probably wrong...was that the first layer height was too close.

Thanks for all the advice, I'll try these suggestions and get back to you.

Colin

Hi all,

Problem is now fixed, two changes in Slic3r, Z-offset was increased to 0.2 mm which is the same as the layer height. Now I can just make out the printer tracks on the bottom of objects. I'm not sure I understand this as first layer should print at 0.2 without adding the offset.

The other change was to the overlap infill/perimeters. This was set to 15%, reducing to zero helped. I think infill overlap was pushing out the sides.

Thanks for help,
Colin

If you set the overlap to zero you should start having problems with the outer walls not being properly attached to the infill. You need the overlap to keep everything glued together. If 15% overlap was pushing out the sides, you have an extruder calibration problem, or the filament diameter was larger than you told the slicer.

---

Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]